TransGo 40-2 Gear Command Shift Kit for Ford C4 1970-81

A 1970s Mustang, Maverick, Comet, early Bronco or light F-series with the C4 three-speed usually shifts soft and slow from the factory, and that long slide between gears is what wears out the intermediate band. The TransGo 40-2 reprogramming kit firms up the shifts on any 1970-and-later C4 while keeping it fully automatic in Drive, and it lets you hold 1st or 2nd to any rpm when you move the lever yourself.

What the 40-2 does in a C4

The C4 is a hydraulically controlled three-speed with ratios of 2.46, 1.46 and 1.00. Shift timing comes from throttle and vacuum modulator pressure working against the governor, and shift feel comes from the springs, accumulator and separator plate in the valve body. The 40-2 changes several of those pieces. It removes the 1-2 accumulator puck and spring, puts new springs on the 2-3 backout, cutback and throttle boost valves, changes the pressure regulator springs, and has you enlarge separator plate holes with the .110 drill supplied. The result is a short, firm shift with the band and high-reverse clutch applying quickly instead of slipping. In the 2 position the trans starts in 2nd and holds it; in 1 it starts in 1st and holds it at any speed.

Symptoms it addresses

• Soft, mushy 1-2 and 2-3 shifts
• Engine flare between gears under load
• Intermediate band or high-reverse clutch wearing quickly
• Upshifts in 1 or 2 when you want to hold a gear for racing or engine braking

How to confirm before you buy

Check the basics first. A cracked vacuum line or a leaking modulator makes a C4 shift harsh and late, and a band that is out of adjustment slips no matter what is in the valve body. TransGo lists line pressure specs for the finished job: Drive at idle 55-65 psi and 150-185 psi at wide open throttle, Reverse at idle 60-110 psi and 240-270 psi at WOT. Our line pressure guide shows how to read them. If the engine slides up in rpm without the car pulling, read Shift Flare vs Slip to sort a worn band from a calibration problem.

Fitment

TransGo states the 40-2 fits all 1970 and later C4 transmissions. It does not fit the C5, which you can spot by its single-bolt filter. Before you start, identify your valve body: on a Type A body a roll pin holds the throttle limit valve, and on a Type B body the filter holds it. The kit includes a separator gasket for each type, and you use the instruction page and pressure regulator springs that match your body. For a 1967-69 C4 with the earlier casting, the TransGo 47-3 is the kit to look at, and it is manual-shift only. More C4 parts are listed in our rebuild kits section.

Install notes

• Reuse one .217 plastic checkball from your old valve body. It is not supplied.
• Type A bodies use the yellow outer and red inner pressure regulator springs. On Type B, use yellow and red for street cars and trucks under 5,500 lb, and green outer with red inner only for full race or vehicles over 5,500 lb.
• Torque small valve body bolts 40-60 in-lb, large bolts 80-120 in-lb, side plate screws 30-35 in-lb and valve body to case 80-120 in-lb.
• Intermediate band: snug, then back off 1-1/4 turns. Reverse band: snug, back off 3 turns. If you feel a brief bind-up on a manual 1-2 shift, back the rear band off one more turn.
• Keep the modulator on manifold vacuum, and set kickdown linkage so you get a 3-2 downshift.
• Do the job with a new filter and pan gasket; if the case is leaking, add a C4 external reseal kit. Many C4s of this era were built for Type F, such as our Type F ATF, but go by your dipstick or rebuilder's spec.

One caution from TransGo: the trans follows your command, so pulling into 2 or 1 at highway speed will downshift right then. Use good judgment.

Will my C4 still shift on its own after this kit?

Yes. The 40-2 keeps the C4 fully automatic in Drive. In 2 it starts and holds 2nd, and in 1 it holds 1st at any speed.

Does it fit a 1968 C4 or a C5?

TransGo says it fits all 1970 and later C4 transmissions, not the C5 (single-bolt filter). For 1967-69 castings, look at the TransGo 47-3.

Which pressure regulator springs should I use?

Type A valve bodies use yellow outer and red inner. Type B bodies use yellow and red for street vehicles under 5,500 lb, or green outer and red inner for full race or vehicles over 5,500 lb.

Do I need to adjust the bands?

Yes. Snug the intermediate band and back off 1-1/4 turns, and snug the reverse band and back off 3 turns. Back the rear band off one more turn if a manual 1-2 shift binds briefly.

What line pressure should I see after install?

TransGo's specs: Drive idle 55-65 psi, WOT 150-185 psi; Reverse idle 60-110 psi, WOT 240-270 psi.

What fluid should I use?

Many C4s of this era were built for Ford Type F. Check the dipstick, and if the unit has been rebuilt, use what the rebuilder specified.

• Checking Transmission Line Pressure
• Shift Flare vs Slip: How to Tell the Difference
• Valve Body Cleaning and Inspection